Warm the milk and pour it into a shallow bowl. Line a 25 × 15 cm pan with parchment paper (optional).
Melt 150 g white chocolate over a double boiler, then let it cool until warm (not hot).
Beat 150 g cream cheese until smooth. Mix in the cooled white chocolate.
Whip 250 ml heavy cream to soft peaks. Fold it into the cream cheese mixture (or mix on the lowest speed) just until combined.
Divide the filling into 3 equal portions.
Dip cocoa biscuits quickly in the warm milk and place them in the pan to make the first layer.
Spread 1/3 of the filling evenly over the biscuits.
Add a second layer of dipped biscuits.
Spread another 1/3 of the filling evenly on top.
Add a third layer of dipped biscuits.
Spread the last 1/3 of the filling evenly on top.
Add a final layer of dipped biscuits on top.
Heat 30 ml heavy cream until just boiling. Pour it over 100 g chopped white chocolate.
Whisk until smooth, then pour the topping over the cake.
Decorate with grated white or dark chocolate if you want.
Refrigerate for 2–3 hours, then slice and serve.